Robots are automated devices that are able to manipulate objects using a series of rigid links, which in turn are interconnected via articulations or motor-driven robotic joints. Each joint in a typical robot represents an independent control variable, also referred to as a degree of freedom (DOF). End-effectors are the particular links used for performing a task at hand, e.g., grasping a work tool or an object. Therefore, precise motion control of a robot may be organized by the level of task specification: object level control, i.e., the ability to control the behavior of an object held in a single or cooperative grasp of a robot, end-effector control, and joint level control. Collectively, the various control levels cooperate to achieve the required robotic mobility, dexterity, and work task-related functionality.
Humanoid robots in particular are robots having an approximately human structure or appearance, whether a full body, a torso, and/or an appendage, with the structural complexity of the humanoid robot being largely dependent upon the nature of the work task being performed. The use of humanoid robots may be preferred where direct interaction is required with devices or systems that are specifically made for human use. Due to the wide spectrum of work tasks that may be expected of a humanoid robot, different control modes may be simultaneously required. For example, precise control must be applied within the different spaces noted above, as well control over the applied torque or force, motion, and the various grasp types.
In order to approximate human movement each major joint within the robot, such as waist or arm joints, requires at least one actuator for each DOF. However, in a multi-fingered hand, it may be advantageous to drive some combinations of finger joints from a common actuator, so that there are fewer actuators than finger joints. Nevertheless, a highly dexterous hand will have a plurality of actuators, perhaps as many as a dozen or more, to enable a variety of grasp configurations and fine manipulation of grasped objects. Additionally, these actuators must be packaged in an arrangement that approximately represents human structure and appearance.